Hydrocarbon cracking in a regenerable molten media

ABSTRACT

Hydrocarbon feedstocks are cracked at elevated temperatures in a regenerable molten media comprising an oxide of phosphorus, such as phosphorus pentoxide, in combination with a critically defined amount of an alkali or alkaline earth metal oxide or hydroxide including mixtures thereof, to produce high yeilds of light olefins, which olefins such as ethylene are useful in the synthesis of polymers and other valuable chemicals. The carbonaceous materials, such as coke, which are formed and suspended in the molten media during the cracking operation are gasified by contacting said carbonaceous materials with a gaseous stream containing oxygen, such as air, steam or carbon dioxide at temperatures of from about above the melting point of said medium to about 3,000*F. in order to regenerate the melt. When the mole ratio of the alkali and alakline earth metal oxide or hydroxide expressed as the oxide thereof to the glass-forming oxide in the melt is maintained in the range of at least about 1, and preferably in the range of from about 1 to about 3, the gasification rate of the carbonaceous materials which are suspended in the molten media is significantly increased while at the same time suppressing the evolution of sulfur oxides from the gasification zone when the hydrocarbon feedstock contains sulfur and when a gaseous stream containing oxygen is employed as the gasifying reagent.

Primary ExaminerDelbert E. Gantz Assistant Examiner S. Berger Attorney,Agent, or FirmDonald C. Caulfield HYDROCARBON CRACKING IN A REGENERABLEMOLTEN MEDIA United States Patent 1 1 1111 3,852,133

Dugan et al. Dec. 3, 1974 HYDROCARBON CRACKING IN [57] ABSTRACTREGENERABLE MOLTEN MEDIA Hydrocarbon feedstocks are cracked at elevatedtem- 75 Inventors; J h D Jame P, Hi i peratures in a regenerable moltenmedia comprising b h f S i ()m i C d an oxide of phosphorus, such asphosphorus pentoxide, in combination with a critically defined amount of[73] Asslgnee: Exxon keseaFcl and Engmeermg an alkali or alkaline earthmetal oxide or hydroxide Company Lmden including mixtures thereof, toproduce high yeilds of [22] Fil d; A 14, 1972 light olefins, Whii holefins such as ethylene are useful in the synthesis 0 polymers andothervaluable chemi- [21] Appl 280182 cals; The carbonaceous materials, suchas coke, which R l d U5, A li i D are formed and suspended in the moltenmedia during [63] Continuatiomimpan of Sen 186,776 Oct 5 the crackingoperation aregasified by contacting said 1971, abandoned. carbonaceousmaterials with a gaseous stream containing oxygen, such as air, steam orcarbon dioxide at 52 0.5. CI 208/114, 48/202, 208/235, temperethres offrom about eheYe the melting Point of 203/249, 260/683 R, 423/563 saidmedium to about 3,000F. in order to regenerate 51 1111. C1 C10g 11/02 eWhen themele ratio the alkali and [58] Field of Search 208/106, 114,125; khhe earth metal exlde or hydrexlde expressed as the 2 0 202 oxidethereof to the glass-forming oxide in the melt is maintained in therange of at least about 1, and prefer- [56] References Cited ably in therange of from about I to about 3, the gas- UNITED STATES PATENTSification rate of the carbonaceous materials which are suspended in themolten media is significantly in- 3,08l,256 3/1963 Hendal 6t al. 208/125creased at the Same time pp g the evolu I h tion of sulfur oxides fromthe gasiflcation zone when 3 745 109 7/1973 Heredy eta'iTII............IIII.... 208 106 the hydrocarbon feedstock contamsSulfur and when a a gaseous stream containing oxygen is employed as theFOREIGN PATENTS OR APPLICATIONS if i reagent 1 386,669 l/l933 GreatBritain 17 Claims, 1 Drawing Figure PATENTEU {15B 3 74 HYDROCARBONCRACKING IN A REGENERABLE MOLTENMEDIA HYDROCARBON CRACKING IN AREGENERABLE MOLTEN MEDIA CROSS-REFERENCE TO RELATED APPLICATION Thisapplication is a continuation-in-part of US. Ser. No. 186,776, filedOct. 5, 1971 and now abandoned.

FIELD OF THE INVENTION kaline earth metal oxide or hydroxide includingmix tures thereof to produce cracked hydrocarbon products such asethylene and carbonaceous materials. The carbonaceous materials such ascoke which are formed during the cracking process are gasified bycontacting said carbonaceous materials in the molten media with agaseous stream containing an oxygen, i.e., air; water,

i.e., steam; or carbon dioxide reagent at elevated temperatures in orderto regenerate the melt. The cracked hydrocarbon products find use in thesynthesis of polymers and other valuable chemicals.

DESCRIPTION OF THE PRIOR ART The thermal cracking of hydrocarbons atelevated temperatures to produce olefinic compounds such as ethylene byemploying a molten salt such as eutectic mixtures of lithium andpotassium-chloride as the heat transfer medium is well-known to the art.The cracking of hydrocarbon feedstocks in molten heat transfer mediasuch as lead to produce ethylene has likewise been disclosed.

However, the molten media which have heretofore been employed to crackhydrocarbons have suffered from one or more disadvantages which hasresulted in limited industrial application of these processes. Thedifficulty primarily encountered in the prior art processes such asmolten lead was the fact that the carbonaceous particles produced duringthe cracking operation were not suspended in the melt, but formed aseparate phase which contaminated the liquid and gaseous products.Further, with molten media that partially suspended the coke, such aslithium-potassium chloride eutectics, the buildup of such carbonaceousmaterial in or above the molten medium necessitated additional stepssuch as to physically remove the carbonaceous particles from the melt.In addition, numerous contacting media have been proposed in theliterature including metals, alloys, slags, basalt and glass (seeCzecho- Slovakian Pat. No. 109,952) in order to effectuate the thermalcleavage of hydrocarbon feedstocks.

Recently it has been suggested that hydrocarbon feedstocks can becracked in a molten salt of either alkali metal carbonate, alkali metalhydroxide, or a mix ture thereof, to form hydrocarbon productscontaining ethylene and thereafter regenerating the molten salt byintimate contact with oxygen or steam (see US. Pat. No. 3,553,279 andUS. Pat. No. 3,252,774). Such a molten medium, however, suffers from thedisadvantage of undergoing decomposition at operating conditionsnormally employed for cracking hydrocarbon feedstocks, i.e.,temperatures in the range of from about 1,200 to 1,650F. Accordingly,the art is in need of an alternate molten medium which, in addition toproviding the heat transfer medium for the cracking of the hydrocarbonfeedstock, will permit the rapid regeneration of the melt.

In a copending application, U.S. Ser. No. 280,183, filed Aug. 14. 1972,there is described a regenerable molten medium system comprising anoxide of phosphorus in combination with an alkali or alkaline earthmetal oxide(s) or hydroxide(s) which molten medium, in addition toproviding the heat transfer media for the cracking of the hydrocarbonfeedstock, permits the rapid regeneration of the melt by contacting thecarbonaceous material present in the melt with a gasification reagentsuch as air. It has now been discovered that when the mole ratio of thealkali and/or alkaline earth metal oxide and/or hydroxide component(s)expressed as the oxide thereof to the oxide of phosphorus component(s)in'the melt is maintained within a critically defined range thereoccursan unexpected increase in the gasification rate of thecarbonaceous materials present in the melt so as to accelerate theregeneration of the molten medium, while at the same time suppressingthe evolution of sulfur oxide during the gasification' of thecarbonaceous material with a reagent containing oxygen.

SUMMARY OF THE INVENTION It has now been discovered that hydrocarbonfeedstocks are converted to produce high yields of light olefins such asethylene by a process which comprises contacting the hydrocarbonfeedstock with a regenerable molten medium, as hereinafter defined, at atemperature in the range of from about above the melting point of themedium to about 2,500F. for a time sufficient to form crackedhydrocarbon products and carbonaceous materials. Thereafter, thecarbonaceous materials formed and suspended in the molten medium duringthe cracking operation are contacted wit a gaseous stream containing asa reagent oxygen, e.g.,- air, steam or carbon dioxide, includingmixtures thereof, at a temperature in the range of from about themelting point of said medium to about 3,000F. for a period of time inorder to regenerate the molten media. The regenerable molten media ofthe instant invention comprises an oxide of phosphorus such asphosphorus pentoxide (P 0 phosphorus tetroxide (P 0 phosphorus trioxide(P 0 and the like including mixtures thereof in combination with one ormore alkali or alkaline earth metal oxide(s) or hydroxide(s) includingmixtures thereof.

The oxide(s) of phosphorus are employed in combination with an alkali oralkaline earth metal oxide or hydroxide, including mixtures thereof, tocomprise the molten media which is initially charged to the crackingzone. The preferred alkali metal oxides or hydroxides include sodium,potassium, lithium, cesium and mixtures thereof. The preferred alkalineearth metals which are introduced into the cracking zone in either theircorresponding oxide or hydroxide form include barium, strontium,calcium, and magnesium. While the alkali earth metal oxides orhydroxidesmay be emmployed alone in combination with a glass-forming oxide, it ispreferred that when employing an alkaline earth metal oxide or hydroxidein the molten media system of this invention that alkali metal oxides orhydroxides be present in order to lower the melting point of the moltenmedia to that temperature range which is preferred for conducting thecracking or gasilication of a hydrocarbon feedstock.

The mole ratio of the alkali metal compound, that is the mole ratio ofthe alkali metal(s) and/or alkaline earth metal(s) oxide and/orhydroxide to the'oxide(s) of phosphorus is an important feature of theinstant ining reagent, such as air, in order to burn off thecarbonaceous materials and thus regenerate the melt. In addition, bymaintaining the mole ratio within this range, it has been discoveredfurther that the sulfur emissions in the flue gas during gasification-ofthe carbonaceous materials with a gaseous stream containing oxygen,i.e., air, are significantly reduced. Furthermore, maintaining the moleratio below about 3.0, and preferably belowabout 2.5, minimizes carbondioxide emissions from the cracking zone.

As mentioned above, the mole ratio of the alkali metal compound isdefined in terms of the oxide(s) of the alkali or alkaline earthmetal(s) that is employed in combination with the oxide of phosphorus.The basis for defining the mole ratio of the alkali metal compound interms of its oxide form, i.e., expressed as the oxide(s) thereof, is thefact that the alkali metal constituent of the alkali metal oxide(s),e.g., lithium oxide (Li O), alkaline earth metal oxide(s), e.g., bariumoxide (BaO) and alkaline earth metal hydroxide, e.g., barium hydroxideBa(Ol-I) all possess a total number of equivalents of alkali metal oralkaline earth metal of two. The total number of equivalents of alkalimetal in an alkali metal hydroxide, e.g., lithium hydroxide (LiOH),however, is one. Accordingly, it has been discovered that when an alkalimetal hydroxide is employed as an alkali metal compound in combinationwith an oxide of phosphorus to comprise the molten media of the instantinvention, it is necessary to employ two moles of alkali metalhydroxide(s) for each mole of the oxide of phosphorus in order toachieve the same advantages exhibited by a molten media containing anoxide of phosphorus in combination with one mole of either an alkalimetal oxide, alkaline earth metal oxide or alkaline earth metalhydroxide. Therefore, it is evident that it is necessary to employ twiceas many moles of an alkali metal hydroxide as compared to alkali metaloxides or alkaline earth metal oxide(s) or hydroxicle(s) in order toachieve the identical mole ratio of alkali metal compound to the oxideof phosphorus. Hence, when the mole ratio of the'alkali metal compoundis expressed as the oxide of the particular alkali or alkaline earthmetal employed, the singular effect is that the number of moles ofalkali metal hydroxides that are employed in the molten media must bedivided oxides and hydroxides in order to determine the total number ofmoles of alkali metal compound expressed as oxide that are employed in aparticular molten media. Thereafter, the total number of moles of thealkali metal compound isv divided by the total number of moles of theoxide(s) of phosphorus that is present in the molten media in order todetermine the mole ratio of the alkali metal compound to the oxide(s) ofphosphorus component in the melt. I

The advantage of cracking a hydrocarbon feedstock in theabove-mentionedmolten medium resides in the ability of the molten mediaof this invention to: (a) suspend the carconaceous materials formed insitu during the cracking operation uniformly throughout the melt, and(b) thereafter, upon contact with a gaseous stream containing oxygen orsteam at elevated temperature, to promote the rapid gasification of saidcarbonaceous materials. Accordingly, the instant invention permitsfides,the molten medium of the instant invention offers the additionaladvantages of significantly lowering the emission of pollutants into theatmosphere by absorbing the sulfur compounds produced during the burningof the carbonaceous materials with a gasifying reagent containingoxygen. Further, sulfur impurities initially present in the hydrocarbonfeedstock are retained by the molten media of the instant invention inview of the by two and the combined with the total number of moles ofalkali metal oxides and alkaline earth metal fact that a major portionof the hydrogen sulfide formed during the cracking operation is retainedby the melt, particularly when the cracking step is conducted in theessential absence of steam. Also, a portion of the sulfur impuritiesthat are present in the carbonaceous materials are believed to beleached out of the carbonaceous materials by the molten media of theinstant invention, thereby effectuating a further removal of sulfur fromthe carbonaceous materials; Furthermore, the molten media of the instantinvention: (a) have a sufficiently low melting point and possess asuitably wide liquid range to permit a wide range of operatingtemperatures to be employed; (b) possess good thermal conductivity toallow efficient heat transfer, and (c) possess high stability such as toundergo essentially no decomposition to volatile products under highseverity cracking and/or gasification conditions. Thus, it is evidentthat these advantageous properties exhibited by the stable molten mediumof the instant invention offer significant advantages in the thermalcracking of hydrocarbon feedstocks.

Individual, regenerable, stable molten systems that are preferredconsist of phosphorus pentoxide employed in combination with an alkalimetal oxide(s) or hydroxide(s), including mixtures thereof, wherein themole ratio of the alkali or alkaline earth metal oxide or hydroxidecomponent expressed as the oxide thereof to phosphorus pentoxide is inthe range of from at least I to about 3. The most preferred melt systemsof the instant invention comprise phosphorus pentoxide as the phosphorusoxide component in combination with either sodium oxide, potassiumoxide, or lithium oxide and mixtures thereof, as the alkali metal oxidecomponent wherein the mole ratio of the alkali metal component expressedas the oxide thereof to phosphorus pentoxide is at least 1 andpreferably from 1.5 to about 3.

It is to be understood that it is clearly within the scope of thisinvention to employ and define the molten phosphate melts of thisinvention with respect to the salt formed when an oxide of phosphorus isheated to the molten state in combination with an alkali or alkalineearth metal oxide or hydroxide. For example, a molten medium consistingof sodium oxide as the alkali metal oxide and phosphorus pentoxide asthe oxide of phosphorus can also be expressed in the molten state as aphosphate, specifically sodium metaphosphate, on the basis of thefollowing reaction:

Na O P 2NaPO Accordingly, it is to be noted that any of the moltenphosphate melts of this invention may be prepared by fusing anycombinations of raw materials .which, upon heating, form a molten tenmedium containing an oxide of phosphorus in combination with an alkalimetal oxide. wherein the mole ratio of the alkali or alkaline earthmetal oxide or hydroxide to phosphorus oxide is residua, crude bottoms,pitch, asphalt, other heavy hydrocarbon pitch-forming residua, coal,coal tar or distillate, natural tars including mixtures thereof.Preferably, the hydrocarbon feedstock'which is cracked in the stablemolten media of the instant invention comprises a hydrocarbon feedstockwhich contains material boiling above about 400F. at atmosphericpressure. The.

preferred hydrocarbon feedstocks which can be employed in the practiceof the instant invention are crude oils, aromatic tars, and atmosphericor vacuum residua containing material boiling above about 650F. atatmospheric pressure. Aromatic tar, atmospheric or vacuum residua orparticularly preferred.

While not essential to the reaction, an inert diluent can be employed inorder to regulate the hydrocarbon partial pressure in the molten mediacracking zone. The inert diluent should normally be employed in a molarratio of from about 1 to about 50 moles of diluent per mole ofhydrocarbon feed, and more preferably 1 to 10. Illustrative of thediluents that may be employed are helium, carbon dioxide, nitrogen,steam, methane and the like.

This invention will be further understood by reference to theaccompanying drawing which is a schematic flow diagram for thermallycracking a heavy hy drocarbon feedstock in the molten media of theinstant invention.

A heavy hydrocarbon residua fraction having a boiling point atatmospheric pressure of above 650F. and Conradson carbon content of 12is passed by way of line 1 into the cracking zone 2. Within the crackingzone 2 is maintained a molten bed containing phosphorus pentoxide as theoxide of phosphorus in combina- 6 tion with lithium and potassium oxidewherein the mole ratio of lithium oxide to potassium oxide is 60 to 40and the mole ratio of lithium and potassium oxide to boron oxide isabout 1.2. The liquid hydrocarbon feedstock passing by way of line 1 isintroduced into the cracking zone 2 by bubbling the feedstock throughthe molten media 3. Alternatively, the molten media may be sprayed intothe reactor or trickled down the reactor walls as the hydrocarbonfeedstock passes throughthe reactor. The molten media may flow eithercocurrently or countercurrently to the flow of the hydrocarbonfeedstock.

The temperature of the molten media 3 is maintained in the range of fromabout l,200 to about 2,000F.', and more preferably from about l,300 toabout 1,700F. in order to form cracked hydrocarbonproducts andcarbonaceous materials. Thetemperature of the molten media is maintainedwithin the abovementioned range due to the exothermic gasificationreaction of the carbonaceous materials formed during the crackingreactionfas will be hereinafter described, such that the molten mediaprovides the heat for the cracking operation. Depending upon thetemperature and the specific type of hydrocarbon feedstock, the rate atwhich the feedstock is passed via line 1 into cracking zone 2 is in therange of from about 0.1 to about w./w./hr. (weight of feed/weight ofmelt/- hour), and more preferably from about 0.l to about 20 w./w./hr.Pressures are not a critical feature of the instant invention such thatthe reaction may be conducted at a pressure ranging from subatmospheric,e. g., 0.1 atmosphere to about 50 atmospheres, preferably from about 1to about 10 atmospheres. The reaction time, as expressed in the amountof time the feedstock is in contact with the melt 3, i.e., residencetime, is in the range of from about 0.01 to about 20 seconds, and morepreferably from about 0.3 to about 5.0 seconds.

Thereafter, the cracked products are further cooled to condense andseparate liquid products from the gaseous products containing lightolefms by passing the quenched products by way of line 6 to afractionation zone, not shown. Most of the hydrogen sulfide formedduring the cracking operation is absorbed by the melt, particularly whenthe cracking operation is conducted in the absence of significantamounts of steam. The product distribution obtained by cracking ahydrocarbon feedstock in themanner described above is substantiallyidentical to the product distribution obtained by subjecting the samefeedstock, under identical conditions, to the well-known steam crackingprocess.

The significant advantage of employing the molten media of the instantinvention is that the carbonaceous materials which are formed during theabove-described cracking process become uniformly suspended throughoutthe melt and can be gasified, i.e., burned to gaseous products, whencontacted with a gasifying reagent such as an oxidizing gas, i.e., air,steam or carbon dioxide at elevated temperatures in order to rapidlyregenerate the molten media. Accordingly, the molten carbon feedstockbeing pyrolyzed and the rate at which the feedstock is being introducedinto the cracking zone 2.'Preferably, a vapor lift is employed in orderto circulate the molten media by way of line 7 from the cracking zone 2to the gasification zone 8.

The carbonaceous materials which are formed during the thermal crackingreaction may be generally described as solid particle-like materialshaving a high carbon content such as those materials formed during hightemperature pyrolysis of organic compounds and normally referred to ascoke. While the carbonaceous material heretofore discussed has beenproduced in situ during the cracking of a hydrocarbon feedstock, asdescribed above, it should be emphasized that it is clearly within thescope of theinstant invention to gasify carbonaceous materials which maybe added, in conjunction with or independently of a thermal crackingreaction, to the molten media of the instant invention in the form ofcoal of various grades, polygnite, lignite coal,

coke of various types such as coal coke and petroleum coke, peat,graphite, charcoal and the like. Accordingly, the term gasification asused herein describes the contacting of such carbonaceous materials inthe mol-' ten media of the instant invention with a gasifying reagentcomprising a gaseous stream containing oxygen, steam, carbon dioxide andmixtures thereof. The gasification reaction is carried out by contactingthe carbonaceous material in the molten media 9 with the gasifyingreagent introduced into the gasification zone 8 by way of line 10. Thegasification reaction is carried out at temperatures in the range offrom about the melting point of the molten media to 3,000F. or higherand at a pressure in the range of from subatmospheric to about 100atmospheres-Preferably, the temperature at which the gasificationreaction is carried out is'in the range of from about l,200 to about2,000F., and

more preferably from about 1,400 to about 1,800F.

and more preferably from about 50 to about 100 weight percent. The steamis normally introduced by way of line 10 at a temperature in the rangeof from about 300 to about l,000F., and at a pressure in the range offrom about 100 to about 500 psig in order to regenerate themolten'media. In the event a gaseous stream containing carbon dioxide isemployed as the gasifying reagent, the amount of carbon dioxide thatmust be present in the gaseous stream is in the range of from about 10to about lOO weight percent. Preferably, the temperature and pressure atwhich carbon dioxide is introduced into the gasification zone 8 is inthe range of from about l00 to about l,000F. and 100 to about 1,000psig, respectively. Y

Thespecific gasification rate of the carbonaceous materials inindividual stable, regenerable molten media, as defined bythe amount ofcarbonaceous material which is gasified per hour per cubic foot of melt,is dependent upon the temperature at which the gasification process iscarried out, as well as the residence time of the oxygen containing gasor steam in the melt, the concentration of carbonaceous material in-themelt, and feed rate of oxygencontaining gas into the media. As a generalrule, thecarbon gasification, rate increases as the temperatuare of themelt, concentration of carbonaceous materials and feed rate of theoxygen containing gas increase. Preferably, the concentration ofcarbonaceous materials in the molten medium is maintained in the rangeof from 0.1 to about 60 weight percent, and more preferably from aboutvl .0 to about 20 weight percent, in orderto effecta rapid gasificationthereof. v v p The gaseous products produced by contacting thecarbonaceous materials in the molten glass media with either anoxidizing gas, steam or CO are recovered I from the gasification zone byway ofline 11. When It ispreferred to maintain the pressure in thegasification zone in the range of from'l to about l0 atmospheres.-

When a gaseous stream containing oxygen is employed as the gasifyingreagent in order to regenerate the molten media, the amount of oxygenwhich must be present in the gaseous stream is in the range of fromabout 1 to about lOO weight percent oxygen, and more preferably in therange of from about 10 to about 25 weight percent oxygen. Normally, thegaseous stream containing oxygen is passed through the molten media 9 ata rate of less than about 0.0l w./w./hr. (weight of oxygen/weight ofmolten media/hour) to about 50 w./w./hr., and more preferably from about0.1 w./w./hr. to about 10 w./w./hr. Most preferably, air is introducedby way of line 10 at a temperature in the range of from about 100 toabout 1,000F. in order to effect a rapid regeneration of the moltenmedia.

Alternatively, a gaseous stream containing steam or carbon dioxide mayalso be introduced as the gasifying reagent by way of line 10 into thegasification zone 8 in order to regenerate the molten media. When steamis employed as the gasifying reagent, the amount of steam which must bepresent in the gaseous stream is in the range of from about 10 to I00weight percent,

steam is employed as the gasifying reagent, a hydrogenrich gaseouseffluent is produced and recovered by way of line 11. The contacting ofthe carbonaceous materials with steam under the preferred conditions oftemperature and pressure for regenerating the molten media of theinstant invention, normally I l ,500F. and atmospheric pressure,respectively, result in a gaseous effluent containing about mole percenthydrogen and about 24 mole percent carbon oxides. f

As opposed to the production of either a hydrogen or methane-rich steamwhen steam is employed as the gasifying reagent, the use of anoxygen-containing gas such as air as the gasifying reagent results inthe formation of a nitrogen-rich gaseous effluent. As mentioned above,when air is employed as the gasifying reagent, it has surprisingly beendiscovered that the mole ratio of the alkali component to the oxide ofphosphorus significantly affects the amount of sulfur oxides .that arepresent in the gaseous effluent recovered from the gasification zone.Accordingly, when the mole ratio of the alkali or alkaline earthcomponent to the oxide(s) of phosphorus is at least 1, as defined above,it has been discovered that the emissions of sulfur oxides,predominantly in the form of sulfur dioxide in the flue gas, i.e.,gaseous effluent, from the gasification zone is drastically reduced.

Thus, it is evident that the practice of the process of the instantinvention offers the further advantage of removing objectionablecontaminants such as sulfur impurities which are inherently formedduring the pro cessing of heavy hydrocarbon feedstocks. During thegasification of the carbonaceous materials with an oxidizing gas such asair, it is believed that the sulfur impurities present in thecarbonaceous material are oxidized to sulfur oxides and are abosorbed bythe molten media of the instant invention. In addition, the process ofthe instant invention further serves to remove other contaminantspresent in a heavy hydrocarbon feedstock such as ash forming impuritieswhich include trace metals such as vanadium, iron and nickel that arenormally present to a greater or lesser degree depending on the specifictype of hydrocarbon feedstock being cracked and/or gasified.

The melt which has been regenerated as described above in gasificationzone 8 is withdrawn by way of line 12 and reintroduced back into thecracking zone 2. Normally, the amount of carbonaceous material that isgasified in the gasification zone 8 is substantially equivalent to theamount of carbonaceous material being formed during the crackingoperation in the cracking zone 2, such that an overall balance ofcarbonaceous material is maintained throughout the. system. A furtheradvantageof employing a gaseous stream containing oxygen as thegasifying reagent is the fact that the gasification, i.e., burning ofcarbonaceous materials with oxygen, is an exothermic reaction. Thus,when an oxidizing gas such as air is employed to gasify the carbonaceousmaterials in gasification zone 8, a sufficient amount of heat isliberated in order to provide an overall heat balance for both thegasification and cracking processes. Accordingly, in additiontoregenerating the melt, the gasification of the carbonaceous materialswith an oxidizing gas maintains the temperature of the melt such thatthe melt being passed by way of line 12 into the cracking zone 2provides the heat required for the thermal cracking of the hydrocarbonfeedstock.

As can be appreciated, while the molten media of the instant inventioneffectuates the removal of sulfur and ash-forming impurities from thecarbonaceous materials by absorbing these impurities during thegasification of the carbonaceous materials with an oxygen containinggasifying reagent, the continual buildup of these impurities in the meltrequires that a slip-stream be withdrawn from 'the integrated crackingand gasification processes described above in order to restore the levelof these impurities present in the melt to an acceptable level. Whilethe slip-stream may be withdrawn from either the cracking orgasification zone or from any of the transfer lines wherein the moltenmedia is being passed to either the cracking or gasification zone, i.e.,lines 7 and 12, respectively, it is preferred to withdraw a stream ofthe molten media from transfer line 7. The basis for this preference ofremoving a portion of the contaminated molten media from the crackingzone resides in the fact that the cracking zone contains a greateramount of carbonaceous material, which carbonaceous material effects thereduction of alkali or alkaline earth metal sulfur oxides to metalsulfides, thereby facilitating the subsequent removal of the sulfur fromthe molten media, as will be hereinafter described.

The sulfur impurities present in the carbonaceous material as mentionedabove are retained by the molten media during gasification with anoxidizing gas stream as well as being'leached from the coke by the meltat elevated temperatures. When steam is employed as the gasifyingreagent, however, the sulfur impurities are not converted to sulfuroxides and are not absorbed by the melt but rather the sulfur incarbonaceous material is primarily converted to hydrogen sulfide and isrecovered in the effluent from the gasification zone. Thus, when anoxidizing gas stream is employed as the gasifying reagent, the sulfurimpurities are absorbed by the melt in the form of metal sulfites orsulfates. The presence of carbonaceous materials in the molten mediaserves to reduce the metal sulfites or sulfates, predominantly alkali oralkaline earth metal sulfites, to their sulfide form. The metal sulfidesare thereafter contacted with a carbon dioxide and water in order torecover the sulfur impurities as hydrogen sulfide. Accordingly, aslip-stream 13 is withdrawn from line 7 and is passed to a sulfurrecovery zone 14, wherein carbon dioxide and steam is introduced by wayof line 15 and passed through the melt 16 at a temperature in the rangeof from about 800 to about l,800F. Alternatively, the molten mediacontaining the sulfur impurity as a metal sulfide is passed into asulfur recovery zone and is contacted with water in order to dissolvethe melt and recover precipitated metals and ash and thereafter carbondioxide is bubbled through the solution in order to recover the sulfurimpurity as'a hydrogen sulfide rich stream. In either embodiment, it isessential that the sulfur impurities be present in the sulfide formbefore being contacted with water or steam and carbon dioxide. In theevent that a sufficient amount of carbonaceous material is not presentin the system described above, and specifically in the cracking zone 2in order to reduce the metal sulfate and sulfite to their sulfide form,it may be necessary to employ a reducing zone prior to passing themolten media into the sulfur recovery zone 16. If a reducing zone isrequired, it is evident that the slip-stream may be withdrawn from anypoint in the system and thereafter passed to the reducing zone whereinsuch reducing agents as carbon, hydrogen, carbon monoxide, methane,ethane or the like may be employed in order to reduce the metal sulfiteor sulfates to their sulfide form. If such a reducing zone is required,it is preferred to have a holding zone below the cracking zone whereinthe addition of further amounts of carbonmay or may not be necessary,depending on the specific type of hydrocarbon feedstock, to effectuatethe reduction of substantially all of the metal sulfate or sulfites totheir sulfide form.

The hydrogen sulfide rich stream is recovered from the sulfur recoveryzone by the way of line 17 and may be ultimately passed to a Claus plantfor sulfur recovery. The molten media with a reduced sulfur content iswithdrawn from the sulfur recovery zone by way of line 18, wherein thismolten media containing a reduced sulfur level is returned to thegasification zone by way of line 19.

it will, likewise, be necessary to treat the molten media in order toremove trace metals and ash which have accumulated in the melt.Accordingly, a stream of the melt with a reduced sulfur content iswithdrawn by way of line 20 from line 18 and is passed to an ashrecovery zone, not shown, wherein the ash is separated from the melt bydissolution in water.

While the initial charge of the molten media to the cracking zone mayconsist solely of an alkali or alkaline earth metal oxide or hydroxidein combination with an oxide of phosphorus as described above, it is tobe understood that the cracking and gasification of a heavy hydrocarbonfeedstock in such a molten media in accordance with the processingscheme disclosed above will necessarily result over a prolonged periodof time in varying the overall composition of the melt. For example,during the gasification when an oxygen containing gas is employed togasify the carbonaceous materials present in the melt, a portion of thecarbon dioxide that is formed during combustion, i.e., the gasificationreaction, is absorbed by the melt. A fraction of this portion of carbondioxide that is absorbed by the melt forms a carbonate in the melt, andpredominantly an alkali or alkaline earth metal carbonate depending uponthe specific alkali or alkaline earth metal oxide or hydroxide that isemployed as the alkali or alkaline earth metal component of the moltenmedia of the instant invention. The extent of the absorption of carbondioxide by the molten glass media and thus the amount of carbonate thatis formed in the melt of the instant invention is a function of the moleratio of the alkali metal component to the glassforming component, the

specific alkali metal component employed, as well as the temperature ofthe melt and the carbon dioxide partial pressure existing overthe bed ofthe molten media. As mentioned above, after a prolonged period ofconducting the gasification process in the molten media of the instantinvention such as will occur in a commercial unit, an equilibriumcarbonate concentration will exist in the melt. The equilibriumcarbonate concentration in any glass-forming melt will generallyincrease as the mole ratio of alkali metal oxide or bydroxide to theglass-forming oxide increases, as the molecular weightof the cationincreases, i.e., a melt containing potassium will absorb more carbondioxide than i a melt containing sodium, and a melt containing sodiumwill absorb more carbon dioxide than a melt containing lithium. Thecarbonate concentration predominantly in the form of alkali or alkalineearthmetal carbonates in molten media of the instant invention ispreferably kept to a minimum and, depending on the factors indicatedabove, will comprise below about 30 weight percent of the melt,preferably below about20, and more preferably below about 15 weightpercent of the melt. i

In addition, the continuous melt cracking and gasification process ofthis invention will result in the composition of the molten media beingeffected by the presence of alkali or alkaline earth metal sulfates,sulfites and sulfides, as mentioned above, as well as with ashcomponents, including that amount of residual carbonaceous material thatmay be tolerated in the melt. Accordingly, the steady state compositionof the molten media will normally contain, in addition to the alkali andalkaline earth metal carbonates referred to above, from about 10 toabout 20 weight percent sulfates, to about 10 weight percent metalsulfites, 0 to about 10 weight metal sulfides, from 3 to about 5 weightpercent carbonaceous materials and from about 2 to about weight percentash. As will be appreciated, the melt composition will vary from thegasification zone to the cracking zone as well as in the reducing andsulfur recovery zones. For example, while the metal sulfate may bepresent in the melt in the gasification zone in an amount in the rangeof from 10 to weight percent, the amount of metal sulfate in thecracking, reducing and sulfur recovery zones will normally vary fromabout 0 to about 10 weight percent. Likewise, whereas the amount ofmetal sulfide in the cracking, reducing and sulfur recovery zones is inthe range of from about 5 to about 20 weight percent, the amount ofmetal sulfide in the melt in the gasification zone is normally inthe'ran'ge of from about 0 to about 10 weight'percent. Thus, aftercontinuous practice of the cracking and gasification process describedherein, the amount of alkali and alkaline earth'phosphorus compound suchas alkali metal phosphate that is present in the melt will normallyconstitute from about 15 to about 85 weight percent of the melt,preferably at least about 30 weight percent, and more preferably atleast about 50 weight percent of the molten media. It is to beunderstood, however, that the only requirement of the molten media ofthis invention is-that said molten media contain a sufficient amount ofan alkali or alkaline earth metal oxide or hydroxide, including mixturesthereof in combination with an oxide of phosphorus, to be regenerable,that is both suspend the carbonaceous materials formed during thecracking reaction uniformly throughout the melt and thereafter promotethe rapid gasification of such carbonaceous materials upon contact witha gasifying reagent such as air or steam at elevated temperatures.

It should be noted that the presence of such alkali and alkaline earthmetal sulfides,-sulfates, sulfites, carbonates as well as ash componentsin the molten media of the instant invention will effectively alter, toa slight degree, the mole ratio of the alkali or alkaline earth metaloxide or hydroxide compound to the oxide of phosphorus component fromthe initial mole ratio of the .molten media that was initially chargedto the cracking zone. Forexample, the existence of an equilibriumcarbonate concentration in the molten media as well as the presence ofmetal sulfates and sulfides will effectively lower, to a slight degree,the initial mole ratio of alkali or alkaline earth metal-oxide componentto the oxide of phosphorus component which was charged to the crackingzone. Accordingly, the critical mole ratios disclosed and claimed hereindefine that mole ratio(s) of the alkali and alkaline earth metal oxideor hydroxide to the glass-forming oxide that must be maintained in themolten media in the cracking and gasification zones, in the presence ofthe abovementioned carbonate and sulfur compounds, ash components, andthe like, ,in'order to obtain the advantages of the instant invention.By this is meant that after continuous cracking and gasificationoperation wherein a buildup of contaminants such as sulfur compounds,coke, ash and the like occurs in the melt, the mole ratio of alkalimetal compound to oxide of phosphorus component does not include thatamount of alkali metal compound that is present in these contaminants.Ac cordingly, due to the buildup of these contaminants in the melt andthe loss, to a slight degree, of a small amount of alkali metal compoundand thus a slight reductionin the mole ratio of the alkali metalcompound to the oxide of phosphorus compound, it may be necessary to addadditional amounts of alkalimetal compound to the melt in order tomaintain a specific mole ratio of the alkali metal compound to the oxideof phosphorus in the melt.

This invention will be further understood by reference to the followingexamples.

EXAMPLE 1 A heavy residua hydrocarbon feedstock containing materialsboiling above 650F. was introduced by means of a pump at a rate of about2 grams per minute through a A inch inlet tube into a reactor containinga molten medium consisting of equimolar amounts of phosphorus pentoxideand sodium oxide. The cracking zone was 2 inches in diameter and 12inches in length, and was placed in a Lindberg furnace. The melttemperature was measured by a thermocouple inserted into a thermowellpositioned in the center of the molten media connected to a portablepyrometer. The effluent gases were passed directly to a gaschromatograph for analysis. The quantity of C;- liquid products andcarbonaceous material, namely coke, produced was also measured.

TABLE I RESID CRACKING IN MOLTEN MEDIA steam results in a hydrogen-richgaseous effluent, while the gasification of the carbonaceous materialwith air as the oxygen-containing gas stream results in a nitrogen-richgaseous effluent. Furthermore it can be seen that the carbonaceousmaterials were converted to their respective gaseous streams at highconversions.

EXAMPLE 2 This example indicates the significant increase ingasification rate of the carbonaceous materials present in a moltenphosphate melt when the mole ratio of the alkali or alkaline earth metaloxide or hydroxide component to the oxide of phosphorus is at least one(R l TABLE III Melt Temperature. F. Feed (g) Product Yield, Wt. 72 onFeed Hydrogen Methane Ethylene Ethane Propane Propylene C ConversionButanes i-Butylene n-Butylenes Butadiene Total C,

Total C; Liquid Coke Wt. Balance NaPO As can be seen from the results asshown in Table I, the cracking of a heavy hydrocarbon feedstock in amolten sodium metaphosphate melt results in a high conversion to Cproducts.

As discussed above, the carbonaceous particles which are formed duringthis cracking reaction become dispersed in the molten phosphate media.The specific operating conditions employed and the results obtained ingasifying these carbonaceous materials which become dispersed in themelt with air and steam as the gasifying reagent are set forth in thefollowing Table II.

TABLE II COKE GASIFICATION As can be seen from the results as shown inTable II, the gasification of the carbonaceous material with EFFECT OFALKALI OXIDE/PHOSPHORUS OXIDE MOLE RATIO ON GASIFICATION RATETemperature: I500F.; Air Flow Rate: 2 STP l/min. 475 grants 60:40 mole7r Lithium: Potassium Phosphate; 5 weight '7: Fluid Coke R Mole RatioAlkali Oxygen Carbon Gasification Rate Oxides to P 0 Conversion 7c(lb./cu.ft./hr.)

As can be seen from the results as shown in Table III, the carbongasification rate increases rapidly with the increase in the mole ratioof alkali metal oxide to phosphorus oxide (R Number). In addition, itwas observed that increasing the R number (R l') likewise results in amore uniform suspension of the carbonaceous materials throughout themolten medium.

EXAMPLE 3 This example indicates the effect of varying the mole ratio ofthe alkali metal component to the oxide of phosphorus on thegasification of carbonaceous materials in molten phosphate melts whenthe molten media is treated with 2 liters per minute under standardconditions of temperature and pressure with a gaseous stream containingten percent carbon dioxide in nitrogen for a period of 2 hours inorder-that the molten media was employed under equilibrium carbonateconditions.

TABLE IV EFFECT OF R NUMBER ON AIR BURNING OF COKE IN PHOSPHATE MELTSMelt: 480 g Li/K Phosphate with Li O/K O mole Ratio equal 40/60;Temperature: I600F.; Air Flow Rate: 4 STP l/min.; Coke: 20 g Fluid CokeMelt pretreated with 2 STP l/min 1071 Co /N for 2 hours R Number OxygenCarbon Burning Rate of Melt Conversion. Z (lh/cu.ft./hr.)

As can be seen from the results as shown in Table IV, above an R number(mole ratio of alkali metal component to the oxide of phosphorus) of onethere occurs a significant increase in the gasification rate ofcarbonaceous materials present in the melt in the same manner as isshown in Table III of Example 2.

What is claimed is:

1. A process for cracking a hydrocarbon feedstock.

which comprises contacting said feedstock with a repound expressed asthe oxide thereof to the oxide of phosphorus is in the range of fromabout 1.2 to about 2.5, at a temperature in the range of from above themelting point of said media to about 3,000F. for a time sufficient toform cracked hydrocarbon products and to uniformly suspend thecarbonaceous materials formed during said cracking operation throughoutthe molten media.

2. The process of claim 1 wherein the temperature of the molten media ismaintained in the range of from about 1,200 toabout 2,000F.

3. The process of claim 2 wherein said molten media contains a carbonateselected from the group consisting of alkali metal carbonates, alkalineearth metal carbonates and mixtures thereof.

4. The process of claim 2 wherein said molten media containscarbonaceous materials and is regenerated by contacting said moltenmedia with a reagent selected from the group consisting of oxygen,steam, carbon dioxide and mixtures thereof at a temperature in the rangeof from about the melting point of said molten media to about 3,000F.

5. The process of claim 4 wherein the hydrocarbon feedstock containssulfur.

6. The process of claim 5 wherein the amount of sulfur present in themolten media is reduced by:

a. contacting the sulfur compounds in the molten media with a reducingagent; and

b. thereafter contacting the reduced sulfur compounds formed in step (a)with carbon dioxide and water to form hydrogen sulfide as a recoverableproduct.

7. A process for cracking a hydrocarbon feedstock which comprisescontacting said hydrocarbon feedstock with a regenerable molten mediacomprising an oxide of phosphorus in combination with an alkali metalcompound selected from the group consisting of alkali metal oxides,alkali metal hydroxides, alkaline earth metal oxides, alkaline earthmetal hydroxides and mixtures thereof wherein the mole ratio of thealkali metal component expressed as the oxide thereof to the oxide ofphosphorus is in the range of from about 1.2 to about 2.5, at atemperature in the range of from about the melting point of said mediato about 2,500F. to form cracked hydrocarbon products and to uniformlysuspend the carbonaceous materials throughout the molten media, andthereafter gasifying said carbonaceous materials formed during saidcracking process by contacting said molten media containing carbonaceousmaterials with a reagent selected from the group consisting of oxygen,carbon dioxide, steam and mixtures thereof at a temperature in the rangeof from about the melting point of said medium to about 3,000F.

8. The process of claim 7 wherein the temperature of the molten media ismaintained in the range of from about 1,200 to about 2,000F.

9. The process of claim 8 wherein said molten media contains a carbonateselected from the group consisting of alkali metal carbonates, alkalineearth metal carbonates and mixtures thereof.

10. The process of claim 9 wherein the gasifying reagent is an oxygencontaining gasstream.

1 1. The process of claim 10 wherein-the hydrocarbon feedstock is aheavy hydrocarbon feedstock containing sulfur.

12. A process for cracking a heavy hydrocarbon feedstock containingsulfur which comprises:

a. contacting said feedstock with a regenerable molten media comprisingan oxide of phosphorus in combination with an alkali metal compoundselected from the group consisting of alkali metal oxides, alkali metalhydroxides, alkaline earth metal oxides, alkaline earth metal hydroxidesand mixtures thereof wherein the mole ratio of the alkali metalcomponent expressed as the oxide thereof to the oxide of phosphorus isin the range of from about 1.2 to about 2.5, at atemperature in therange of from about the melting point of said media to about 2500F. toform cracked hydrocarbon products and to uniformly suspend thecarbonaceous materials throughout the molten media;

b. contacting the molten media'containing said carbonaceous materialswith a gaseous stream cont'aining oxygen at a temperature in the rangeof from about above the melting point of said media to about.3000F. inorder to gasify said carbonaceous products and to form sulfur compounds;

c. contacting the sulfur compounds formed in step (b) in the moltenmedium with a reducing agent; and

d. thereafter contacting the reduced sulfur compounds formed in step (c)with carbon dioxide and water to form hydrogen sulfide as a recoverableproduct.

13. The process of claim 12 wherein said reducing agent is carbon.

14. The process of claim 13 wherein the reduced sulfur compounds formedin step (a) are selected from the group consisting of alkali metalsulfides, alkaline earth metal sulfides and mixtures thereof.

15. The process of claim 14 wherein said oxide of phosphorus isphosphorus pentoxide.

16. The process of claim 15 wherein said molten media contains acarbonate selected from the group consisting of alkali metal carbonates,alkaline earth metal carbonates and mixtures thereof.

17. The process of claim 16 wherein the alkali metal compounds areselected from the group consisting of sodium oxide, potassium oxide,lithium oxide and mixtures thereof.

1. A PROCESS FOR CRACKING A HYDROCARBON FEEDSTOCK WHICH COMPRISESCONTACTING SAID FEEDSTOCK WITH A REGENERABLE MOLTEN MEDIA COMPRISING ANOXIDE OF PHOSPHORUS IN COMBINATION WITH AN ALKALI METAL COMPOUNDSELECTED FROM THE GROUP CONSISTING OF ALKALI METAL OXIDES, ALKALI METALHYDROXIDES, ALKALINE EARTH METAL OXIDES, ALKALINE EARTH METAL HYDROXIDESAND MIXTURES THEREOF, WHEREIN THE MOLE RATIO OF THE ALKALI METALCOMPOUND EXPRESSED AS THE OXIDE THEREOF TO THE OXIDE OF PHOSPHO-
 2. Theprocess of claim 1 wherein the temperature of the molten media ismaintained in the range of from about 1,200* to about 2, 000*F.
 3. Theprocess of claim 2 wherein said molten media contains a carbonateselected from the group consisting of alkali metal carbonates, alkalineearth metal carbonates and mixtures thereof.
 4. The process of claim 2wherein said molten media contains carbonaceous materials and isregenerated by contacting said molten media with a reagent selected fromthe group consisting of oxygen, steam, carbon dioxide and mixturesthereof at a temperature in the range of from about the melting point ofsaid molten media to about 3,000*F.
 5. The process of claim 4 whereinthe hydrocarbon feedstock contains sulfur.
 6. The process of claim 5wherein the amount of sulfur present in the molten media is reduced by:a. contacting the sulfur compounds in the molten media with a reducingagent; and b. thereafter contacting the reduced sulfur compounds formedin step (a) with carbon dioxide and water to form hydrogen sulfide as arecoverable product.
 7. A process for cracking a hydrocarbon feedstockwhich comprises contacting said hydrocarbOn feedstock with a regenerablemolten media comprising an oxide of phosphorus in combination with analkali metal compound selected from the group consisting of alkali metaloxides, alkali metal hydroxides, alkaline earth metal oxides, alkalineearth metal hydroxides and mixtures thereof wherein the mole ratio ofthe alkali metal component expressed as the oxide thereof to the oxideof phosphorus is in the range of from about 1.2 to about 2.5, at atemperature in the range of from about the melting point of said mediato about 2,500*F. to form cracked hydrocarbon products and to uniformlysuspend the carbonaceous materials throughout the molten media, andthereafter gasifying said carbonaceous materials formed during saidcracking process by contacting said molten media containing carbonaceousmaterials with a reagent selected from the group consisting of oxygen,carbon dioxide, steam and mixtures thereof at a temperature in the rangeof from about the melting point of said medium to about 3,000*F.
 8. Theprocess of claim 7 wherein the temperature of the molten media ismaintained in the range of from about 1,200* to about 2, 000*F.
 9. Theprocess of claim 8 wherein said molten media contains a carbonateselected from the group consisting of alkali metal carbonates, alkalineearth metal carbonates and mixtures thereof.
 10. The process of claim 9wherein the gasifying reagent is an oxygen containing gas stream. 11.The process of claim 10 wherein the hydrocarbon feedstock is a heavyhydrocarbon feedstock containing sulfur.
 12. A process for cracking aheavy hydrocarbon feedstock containing sulfur which comprises: a.contacting said feedstock with a regenerable molten media comprising anoxide of phosphorus in combination with an alkali metal compoundselected from the group consisting of alkali metal oxides, alkali metalhydroxides, alkaline earth metal oxides, alkaline earth metal hydroxidesand mixtures thereof wherein the mole ratio of the alkali metalcomponent expressed as the oxide thereof to the oxide of phosphorus isin the range of from about 1.2 to about 2.5, at a temperature in therange of from about the melting point of said media to about 2500* F. toform cracked hydrocarbon products and to uniformly suspend thecarbonaceous materials throughout the molten media; b. contacting themolten media containing said carbonaceous materials with a gaseousstream containing oxygen at a temperature in the range of from aboutabove the melting point of said media to about 3000* F. in order togasify said carbonaceous products and to form sulfur compounds; c.contacting the sulfur compounds formed in step (b) in the molten mediumwith a reducing agent; and d. thereafter contacting the reduced sulfurcompounds formed in step (c) with carbon dioxide and water to formhydrogen sulfide as a recoverable product.
 13. The process of claim 12wherein said reducing agent is carbon.
 14. The process of claim 13wherein the reduced sulfur compounds formed in step (a) are selectedfrom the group consisting of alkali metal sulfides, alkaline earth metalsulfides and mixtures thereof.
 15. The process of claim 14 wherein saidoxide of phosphorus is phosphorus pentoxide.
 16. The process of claim 15wherein said molten media contains a carbonate selected from the groupconsisting of alkali metal carbonates, alkaline earth metal carbonatesand mixtures thereof.
 17. The process of claim 16 wherein the alkalimetal compounds are selected from the group consisting of sodium oxide,potassium oxide, lithium oxide and mixtures thereof.